Lung cancer is the second most common cancer among both men and women. With an overall mortality rate of about 90%, it is the leading cause for cancer deaths for both sexes. Survival from lung cancer is directly related to its size when it is detected. The earlier the detection is, the higher the chances of successful treatment are. The cure rate for Stage I lung cancers is 70-80%. By the time the nodules grow large enough for them to interfere with a patient's breathing, then the time for optimum treatment has passed.
These types of cancers can be detected using medical imaging such as X-rays and CT-scans. They appear as “nodules”, bright circular abnormalities in the X-ray image. Nodules are normally denser than their surrounding tissues. They can vary in size, intensity and contrast levels. On the x-ray they can appear to be located between ribs, on top of ribs, or behind an organ such as the heart.
Most lung nodules do not have any symptoms and are found “accidentally” when a chest x-ray is done for some other reason. When present, these nodules represent cancer about 40% of the time. This percentage is higher in those that are at high risk for lung cancer. The larger the nodules are, the easier they are to detect, and the higher the probability they are due to cancer. The smaller the nodules are, the harder they are to detect. 1 cm is close to the current detection limit.
There are a few diagnostic characteristics that can be used to determine if a nodule is cancerous or not. The larger the nodule, the more likely it is cancerous. Cancerous nodules on average double in size in about 4 months, whereas benign nodules have little or no size change in the same period. Therefore, nodules that grow rapidly are most likely cancerous. The rougher their edges, or the larger they are, the more likely they are to be cancerous. Smooth, round nodules are more likely to be benign, whereas irregular or “spiculated” nodules are more likely to be cancerous. Lung nodules that are calcified are more likely to be benign. Also, lung nodules described as “cavitary,” meaning that the interior part of the nodule appears darker on x-rays, are more likely to be benign.
It is estimated that somewhere between 10 to 20% or more of cancerous chest X-ray nodules are missed on the first reading of the film. The smaller the nodule, the higher the percentage of them are missed. When a second X-ray is taken, and the nodule has grown, then looking back at the earlier X-rays it is normally obvious that the nodule was present, but was missed by the radiologist.
The early detection and diagnosis of pulmonary nodules in chest X-ray image are among the most challenging clinical tasks performed by radiologists. They may or may not seek the aid of methods to digitally enhance the x-rays or automatically detect potential nodules. In test x-rays, current automatic detection methods typically do not identify all known nodules. If their parameters are set such that they do detect all known nodules, then they also will detect many nodules that are false (false positives). How to reduce the number of false positives while maintaining a high true positive detection rate is the most important work in realizing a chest CAD system.
It is apparent that a method to accurately and routinely detect smaller and/or a higher percentage of nodules in chest X-rays, CT-scans, or mammograms has the potential to save lives. We want to detect them when they are small since they can grow so quickly, and that chest x-rays are not taken that often. A lung cancer screening method that can safely and economically detect a large number of potentially curable Stage I lung cancers would be an important public health development. The purpose of this invention is to provide such a technique.
It has been observed that the human visual system in most individuals is very good at detecting symmetry and variations from symmetry within a scene. It is also good at detection of motion and relative motion of objects within a scene.
If you drop a small object on the floor, you might pick up a similar object and drop it as well, watching and listening as it falls. By dropping the known object, we can see (and hear) how it falls, and understand what it looks like against the floor background. Having this reference, and/or the symmetry of two objects on the floor helps in locating the first object. One of the aspects of this invention is to take advantage of the human visual system to see symmetry, asymmetry, and duplicate objects.
The advertising industry takes advantage of the human visualization system's ability to detect subtle and differential motion. For example, in a TV advertisement they will slowly enlarge and move text that they want the viewer to pay the most attention to. We can't help but see the movement, and our attention is drawn to the area of the display where the movement occurs. Differential movement at the same location in a display appears to be more powerful in attracting our attention than just simple movement of one object. This is another feature of the human visualization system that the current invention can capitalize on.